Abstract Human cytomegalovirus (HCMV) transmission from mother to fetus is implicated in ~15% of stillbirths and ~16,000 birth defects annually in the US. HCMV is also the major viral cause of medical complications associated with bone marrow and organ transplantation. Passive immunization using anti-HCMV enriched human immune globulin (HIG) has shown promising activity for both indications. HIG is a complex, variable product that may cause side effects from off-target antibody binding. A monoclonal antibody (mAb) offers qualitative advantages over HIG including potency, safety, production efficiency and quality control. Trellis Bioscience has discovered a high affinity native human mAb (TRL345) against the most conserved site on the HCMV virion (gB AD-2 Site I). TRL345 is a human IgG1kappa (G1m1,17 (z,a); Km3 allotype) monoclonal antibody cloned from human B lymphocytes. This mAb neutralized 15 out of 15 clinical isolates of all four major serotypes. It protected all of the specialized cell types relevant to human pathology. It was also fully protective in a model of human placental fragments grown as tissue explants ex vivo. This published work was completed under a Phase I/II SBIR grant. A Master Cell Bank has been developed that expresses TRL345 in CHO cells at a commercially useful level (1.74 g/L) at the 250L GMP scale. All IND-enabling analytical work has been completed, including GLP toxicology in rats and tissue reactivity profiling. With SBIR CRP funding, the first clinical lot has been manufactured yielding sufficient material for Phase 1 and 2 human clinical trials. We propose here to conduct a Phase 1 single ascending dose clinical trial in healthy volunteers.